Structural sandwich plate members are described in U.S. Pat. No. 5,778,813 and U.S. Pat. No. 6,050,208, which documents are hereby incorporated by reference, and comprise outer metal, e.g. steel, plates bonded together with an intermediate elastomer core, e.g. of unfoamed polyurethane. These sandwich plate systems may be used in many forms of construction to replace stiffened steel plates, formed steel plates, reinforced concrete or composite steel-concrete structures and greatly simplify the resultant structures, improving strength and structural performance (e.g. stiffness, damping characteristics) while saving weight. Further developments of these structural sandwich plate members are described in WO 01/32414, also incorporated hereby by reference. As described therein, foam forms or inserts may be incorporated in the core layer to reduce weight and transverse metal shear plates may be added to improve stiffness.
According to the teachings of WO 01/32414 the foam forms can be either hollow or solid. Hollow forms generate a greater weight reduction and are therefore advantageous. The forms described in that document are not confined to being made of light weight foam material and can also be make of other materials such as wood or steel boxes, plastic extruded shapes and hollow plastic spheres.
WO 02/33200 discloses a riser, in particular a seating riser for a sports stadium, made of structural sandwich plate. The riser comprises upper and lower metal plates bonded together by a solid elastomer core, which may have different thicknesses in the treads and rises. This riser represents a considerable weight saving as compared to conventional stiffened steel or pre-stressed concrete constructions and the inherent vibration damping characteristics of the sandwich plate are an additional advantage.